The guinea pig pneumonia model mimics Legionnaires' disease as seen in immunocompromised humans, with high untreated fatality rates and as such lends itself to studies of experimental chemotherapy. Guinea pig infection is also used to assess relative virulence of different Legionella bacterial strains, and has also been used to study host immune defenses. Here I describe the method used to produce Legionella sp. pneumonia in the guinea pig using the intratracheal infection technique. This method uses directly observed intratracheal injection of a bacterial suspension, requiring surgical exposure of the trachea.